Thank you for the reply, but i implemented it in another way - in the Leads/ListView.aspx i added following code:
if ("searchbasic".Equals(ctlSearchView.SearchMode, StringComparison.InvariantCultureIgnoreCase))
{
Sql.AppendParameterNe(cmd, "Dead", "STATUS");
}
And added method AppendParameterNe which adds parameter with <> (not equals) clause.